Abstract: An image processing device for automatically setting the accumulation time (exposure time) in accordance with the illuminance even in a dark environment and smoothly following the motion of an object. The image processing device includes: gain control means (7) for performing gain control of a video signal from an imaging element (6) which focuses a signal from an iris (2) controlling the light quantity of the optical signal coming from outside and outputs a video signal; signal processing means (9) for signal-processing an output signal from the gain control means (7); and imaging control means (25) for controlling the opening degree of the iris (2), the exposure time of the imaging element (6), and the gain amount of the gain control means according to the video signal from the signal processing means (9).